The present invention relates to an electro-optical unit for scanning the entire lateral surface of articles appearing substantially cylindrical in shape.
The invention finds application to advantage in the tobacco industry, an art field to which direct reference is made in the following specification albeit with no limitation in general scope implied.
In particular the unit according to the invention can be used in cigarette or filter manufacturing machines to inspect the entire lateral cylindrical surface of continuous cigarette or filter rods, or of the discrete lengths cut from such rods.
Referring particularly to cigarette manufacturing machines, it is conventional practice to employ a substantially vertical duct having a bottom infeed end supplied with an ascending and continuous flow of tobacco particles, and a top outlet end directed at an aspirating belt on which a continuous fillet of tobacco filler is formed.
The tobacco filler is deposited by the aspirating belt on a continuous strip of cigarette paper with gummed longitudinal edges supported by a looped conveyor belt, whereupon the paper is forced by this same belt to wrap around the filler, the two gummed edges are brought into overlapping contact and a continuous cigarette rod of substantially cylindrical shape is formed.
The continuous cigarette rod is caused to advance along a substantially rectilinear and horizontal path toward a cutter device with a rotating blade by which it is divided into discrete portions of predetermined and constantly repeated length.
The paper surface of a cigarette rod fashioned in the manner described above may exhibit a variety of flaws, for example: a defective overlapping join between the longitudinal edges of the paper strip, laceration of the paper caused by impurities in the tobacco filler, stains, deformations, etc.
In order to detect such imperfections and others, the prior art embraces the use of electro-optical scanning units; these units typically comprise a support element in the form of a ring through which the cigarette rod is directed, centrally aligned, a first set of optical fiber light guides connected at one end to a single light source, of which the respective opposite ends are distributed uniformly along a peripheral internal surface of the ring in such a manner as to illuminate an annular area of the cylindrical surface presented by the cigarette rod, and a second set of optical fiber light guides with one set of ends distributed uniformly around the peripheral internal surface of the ring in such a way as to pick up the light reflected by the rod, and the opposite ends connected to a sensing device equipped with photosensitive elements, typically photodiodes or phototransistors.
The photosensitive elements of the sensing device are connected electrically to a comparator that will generate an error signal whenever at least one of the photosensitive elements returns an output signal of value different to a selected reference signal.
It happens with units of this type, when defects in the lateral surface of the continuous cigarette rod are detected, that variations in amplitude of the resulting output signals can become confused with certain variations in the background noise that is generated typically by the photosensitive elements in response to vibrations transmitted inevitably by the advancing cigarette rod.
To avoid the eventuality of the comparator giving false error signals, background noise components are generally filtered out by special electronic processing circuits. Nonetheless, the imperfections it is wished to detect are often missed when using such circuits, which also have the disadvantage of being relatively complex.
In addition, there is the drawback that units of the type in question are themselves somewhat costly in overall terms.
The object of the present invention is to provide an electro-optical unit for scanning the entire lateral surface of articles appearing substantially cylindrical in shape, such as will be more simple, more economical and more reliable than those of the conventional type described above.
The stated object is realized according to the invention in an electro-optical unit for scanning the entire lateral surface presented by articles of substantially cylindrical shape advancing along a predetermined path, comprising illumination means located at a scanning station positioned along the selfsame path, of which the function is to shed light on a given annular area of the surface in substantially uniform manner, and, located at the scanning station, television camera type image detection means of which the position relative to the path is such as to allow the acquisition of a direct image from a first portion of the annular area, and reflecting means located on the side of the path opposite to the detection means, embodied and oriented in such a way that at least one image from a second portion of the annular area can be reflected back toward the detection means.